A variable valve timing control apparatus generally includes a drive-side rotary member rotating in synchronization with a rotation of a crank shaft, and a driven-side rotary member arranged coaxially with the drive-side rotary member and rotating in synchronization with a rotation of a cam shaft for opening and closing a valve of an internal combustion engine. A fluid pressure chamber is formed by the drive-side rotary member and the driven-side rotary member. The fluid pressure chamber is partitioned into advanced angle chambers and retarded angle chambers by partition portions arranged at the driven-side rotary member. A hydraulic fluid is supplied to and discharged from the advanced angle chambers and the retarded angle chambers to thereby control a relative rotational phase of the driven-side rotary member to the drive-side rotary member.
In such variable valve timing control apparatus, leakage of the hydraulic fluid between each advanced angle chamber and each retarded angle chamber needs to be avoided. For example, a known variable valve timing control apparatus disclosed in JP2001-132415A (hereinafter referred to as Reference 1) includes a housing serving as the drive-side rotary member and a vane member serving as the driven-side rotary member. Vane portions serving as the partition portions are arranged at the vane member. Seal members are provided at portions of the vane member facing the drive-side rotary member or the driven-side member. Furthermore, seal members are provided and portions of the drive-side rotary member or the driven-side rotary member facing the vane portions.
According to the variable valve timing control apparatus, the drive-side rotary member having a cylindrical shape is generally manufactured by an extrusion molding process. An inner circumferential wall of the extrusion-molded drive-side rotary member is generally weak against wear. Therefore, the wear resistance of the inner circumferential wall is required to increase. Accordingly, according to the variable valve timing control apparatus disclosed in Reference 1, an inner circumferential wall of the drive-side rotary member manufactured by an extrusion molding process is coated with a self-lubricating resin film or anodized aluminum film in order to increase the wear resistance of the inner circumferential wall.
On the other hand, for example, in a case where the drive-side rotary member of the variable valve timing control apparatus disclosed in Reference 1 is manufactured by a die-casting process, the wear resistance of the inner circumferential wall of the die-cast drive-side rotary member is increased compared to the wear resistance of the inner circumferential wall of the extrusion-molded drive-side rotary member. Accordingly, the inner circumferential wall of the die-cast drive-side rotary member does not need to be coated with the self-lubricating resin film or anodized aluminum film for increasing the wear resistance. However, in the case of the die-cast molding of the drive-side rotary member, a tapered portion is formed on the inner circumferential wall of the drive-side rotary member in order that the die-cast drive-side rotary member is easily removed from a die-casting mold. Further, the inner circumferential wall needs to be machined in order to remove the tapered portion from the inner circumferential wall. In the case that the die-cast drive-side rotary member is machined to remove the tapered portion from the inner circumferential wall, cavities formed inside the die-cast drive-side rotary member may be exposed to the outer side, which may result in decreasing a sealing performance of the seal member.
A need thus exists for a variable valve timing control apparatus, which is not susceptible to the drawback mentioned above.